1. Field of the Invention
The present invention relates to a novel monoclonal antibody, more particularly, to a monoclonal antibody which is specific to a polypeptide capable of inducing the interferon-γ (hereinafter abbreviated as “IFN-γ”) production by immunocompetent cells.
2. Description of the Prior Art
It is known that IFN-γ is a protein which has antiviral-, antioncotic- and immunoregulatory-activities, and is produced by immunocompetent cells stimulated with antigens or mitogens. Because of these biological activities, IFN-γ is expected to be used as an antitumor agent from the beginning of the finding, and is studied energetically on clinical trials as a therapeutic agent for malignant tumors in general including brain tumors. IFN-γ preparations now commercially available are roughly classified into 2 groups, i.e. natural IFN-γs produced by immunocompetent cells and recombinant IFN-γs produced by transformants obtained by introducing into microorganisms of the species Escherichia coli DNAs which encode such natural IFN-γs. In the above clinical trials, one of these IFN-γs is administered to patients as an “exogenous IFN-γ”.
Among these IFN-γs, natural IFN-γs are usually produced by culturing established immunocompetent cells in nutrient culture media supplemented with IFN-γ inducers to form IFN-γs, and purifying the formed IFN-γs. It is known that the type of IFN-γ inducers greatly influence the IFN-γ yield, as well as the facility of IFN-γ purification and the safety of the final products. Generally, mitogens such as concanavalin A (Con A), Lens culinaris, Phytolacca americana, endotoxin and lipopolysaccharide are used as an IFN-γ inducer. However, these mitogens have problems related to their molecular varieties and quality changes depending on their origins and purification methods, as well as the difficulty of obtaining a desired amount of preparations with a constant IFN-γ inducibility. In addition, most of these mitogens induce unfavorable side effects when administered to living bodies, and some of them even cause toxicity, so that it is substantially difficult to induce the IFN-γ production by direct administrations to living bodies.
The present inventors found in mouse liver a substance which induces IFN-γ production during their research of cytokines produced from mammalian cells. They isolated the substance by using a variety of purification methods comprising column chromatography as a main technique, and studied the properties and features, revealing that the substance was a protein having the following physicochemical properties:                (1) Molecular weight Exhibiting a molecular weight of 19,000±5,000 daltons on sodium dodecyl polyacrylamide gel electrophoresis (SDS-PAGE);        (2) Isoelectric point (pI) Exhibiting an isoelectric point of 4.8±1.0 on chromatofocusing;        (3) Partial amino acid sequence Having the partial amino acid sequences in SEQ ID NOs:4 and 5; and        (4) Biological activity Inducing the IFN-γ production by immunocompetent cells.        
It can be concluded that it is a novel substance because no protein with these physicochemical properties has been known. The present inventors continued studies on mouse liver cells and have found that the DNA (SEQ ID NO:6) of the substance consists of 471 base pairs and encodes the amino acid sequence in SEQ ID NO:7.
Based on these findings, the present inventors continued studies on human liver cells and have obtained a DNA which encodes another novel substance that induces IFN-γ production by immunocompetent cells. They revealed that the substance is a polypeptide and decoded its DNA and revealed that the polypeptide has the amino acid sequence in SEQ ID NO:1. They introduced the DNA into Escherichia coli to express the polypeptide and obtained the polypeptide in the resultant culture in a considerably high yield. These findings were disclosed in Japanese Patent Application Nos.184,162/94 and 304,203/94, applied for by the present inventors.
As is described above, the polypeptide has a property of inducing the IFN-γ production by immunocompetent cells, and is expected to be used in a variety of fields as an IFN-γ inducer, antiviral agent, antitumor agent, antibacterial agent, immunoregulatory agent, and blood platelet enhancing agent. In general, the developments of methods for efficiently purifying biologically active polypeptides to give a relatively-high purity and those for assaying many samples in parallel are inevitably required when the polypeptides should be incorporated into pharmaceuticals. Although the best material enabling these purification and assay is a monoclonal antibody, none of which specific to polypeptide has been established.